See the unseen: Mesorectal lymph node metastases in prostate cancer

Our study is the first evaluation of nodal metastatic prostate cancer (PCa) to mesorectal lymph nodes (MLN) detected by (68) Ga-PSMA-PET/CT.

We retrospectively analyzed 76 consecutive PCa patients who underwent (68) Ga-PSMA-PET/CT: 61 PCa patients with biochemical recurrence (BCR) after curative treatment and 15 high-risk PCa before primary therapy. We assessed PET-positive MLN, which are indicative for PCa.

We detected PET-positive lesions for PCa in (68) Ga-PSMA-PET/CT in 66 of 76 (87%) patients. Nodal disease was imaged in 47 of 66 (71%) patients. Indicative mesorectal nodal lesions for PCa were detected in 12 of 76 (15.8%) patients. The median number of PET-positive MLN was one per patient. Seven of twelve patients had recurrent PCa after radical prostatectomy with a median PSA value of 1.84 ng/ml (range 0.31-13). Five of twelve patients had untreated first diagnosed high-risk PCa with median PSA value of 90 ng/ml (range 4.6-93) at PET/CT, respectively. For all PET positive MLN a morphological correlate was found in CT (shortest diameter median 4 mm [range 4-21]; longest diameter median 7.5 mm [range 5-25]). After PET/CT, four patients with recurrent PCa received hormonal therapy, one patient was treated with directed radiation therapy of MLN, one patient received chemotherapy, and one patient was treated with pelvic lymph node dissection. Three high-risk PCa patients received hormonal therapy, and two patients were treated with adjuvant hormonal therapy after radical prostatectomy.

Detection and exact location of nodal metastasis for PCa is crucial for the choice of treatment and the patient's prognosis. (68) Ga-PSMA-PET/CT seems to improve the detection of nodal metastasis in PCa, especially concerning mesorectal lymph nodes.